The present invention relates to phosphoric esters
a) obtainable by reacting an xcfx89-hydroxy-functional oligo- or poly(alkyl)styrene with an alkylene oxide to give a poly(alkyl)styrene-block(b)-polyalkylene oxide copolymer and then converting said copolymer into the corresponding phosphoric esters with a phosphorus compound which forms phosphoric esters, up to 100% of the terminal hydroxyl groups of said poly(alkyl)styrene-block(b)-polyalkylene oxide copolymer being reacted to give phosphoric ester groups and the phosphorus atoms, depending on the chosen stoichiometric proportions, being mono- and/or diesterified,
or
b) based on polystyrene oxide-block(b)-polyalkylene oxide copolymers obtainable starting from a monofunctional starter alcohol by sequential addition of styrene oxide and of an alkylene oxide in accordance with the desired sequence and chain length of the individual segments and subsequently by reaction to give the corresponding phosphoric esters, in the manner described in a).
The invention relates, furthermore, to the preparation of these phosphoric esters and to their use as dispersants for pigments and fillers.
For the dispersion of fillers and pigments in liquid media it is common to operate with the aid of dispersants in order to reduce the mechanical shear forces required for effective dispersion of the solids and at the same time to obtain very high degrees of filling.
The dispersants support the disruption of agglomerates, wet and/or cover, as surface-active materials, the surface of the particles to be dispersed, and stabilize the particles against unwanted reagglomeration.
Dispersants have become indispensable for the preparation, for example, of highly concentrated color pastes for the paints and coatings industry, for the preparation of pigment concentrates (masterbatches) for the coloring of articles made of plastic, and for the processing of unsaturated polyester resins (UP resins) which comprise large amounts of calcium carbonate or aluminum hydroxide (ATH) as fillers.
The combination of very high degrees of filling in association with a very low viscosity is of particular interest for the producers and users of these products on primarily economic grounds. In the case of the fillers, these commonly constitute the least expensive formulating component; pigment concentrates are intended by the plastics processor to be used for coloring in very highly concentrated formxe2x80x94that is, as far as possible without additional carrier materials.
Phosphoric esters and their use as dispersants are known and can be found in the prior art. For instance, U.S. Pat. No. 4,720,514 describes phosphoric esters of a range of alkylphenol ethoxylates, which can be used with advantage to formulate aqueous pigment dispersions. Phosphoric esters for similar use are described in EP-A-0,256,427. U.S. Pat. No. 5,130,463 and U.S. Pat. No. 5,151,218 report phosphoric esters based on hydroxy-terminated polyaddition products and polycondensation products, which are used for the preparation of highly filled polyester molding compounds, especially for SMC and BMC formulations (SMC=sheet molding compounds; BMC=bulk molding compounds). Bifunctional phosphoric esters prepared by the Mannich-Moedritzer reaction, and their adsorption characteristics on calcium carbonate, are described in J. Appl. Polym. Sci. 65, 2545 (1997).
The known phosphoric esters, however, have the disadvantage that in general they are not universally applicable since there is in many cases a lack of adequate compatibility between the dispersing additive and binder or between the dispersing additive and the surrounding medium (aqueous or solvent-containing formulations). The chemical composition of the phosphoric esters also has a large part to play: in aqueous formulations it is preferred to use only those phosphoric esters whose molecule carries no additional hydrolyzable functional groups, such as ester or urethane groups. Frequently, high levels of dispersing additives are required in order to suppress the incidence of agglomerates; the degrees of filling which can be achieved are unsatisfactorily low, the stability of the dispersions and thus the permanence of the viscosity is often inadequate, and flocculation and aggregation cannot always be avoided, possibly resulting in visible separation and in flow defects and surface defects.
It is therefore an object of the present invention to overcome a large number of the above disadvantages and in so doing to achieve not only the viscosity reduction of highly filled dispersions that is important for processability but also improved compatibility with the surrounding medium.
This object is surprisingly achieved through the use of phosphoric esters of amphiphilic block copolymers having the characteristic structural feature of a poly(alkyl)styrene segment and/or a polystyrene oxide segment to which a polyalkylene oxide segment is attached.
The invention accordingly provides phosphoric esters of the general formula I 
x is 1 or 2,
n is a number from 2 to 18,
m and
o are each a number from 2 to 100,
k is a number from 2 to 4,
Rxe2x80x3 is H or a linear or branched alkyl radical which may if desired be substituted by additional functional groups, and
Rxe2x80x2 is an alkyl, alkaryl, alkenyl or sulfopropyl radical.
Preferably Rxe2x80x3=H.
Rxe2x80x2 is commonly derived from an alcohol Rxe2x80x2OH which functions as the starter alcohol for the polymerization of the styrene oxide and alkylene oxide.
Examples of the radicals Rxe2x80x2 are the methyl, butyl, stearyl, allyl, hexenyl, nonylphenyl and oleyl radicals.
Methyl and butyl radicals are preferred for Rxe2x80x2.
Where n=2 the polyether radical contains exclusively ethylene oxide units. Where n greater than 2, the polyether radical consists of ethylene oxide units and, proportionally, of oxyalkylene units whose carbon number is between 3 and 18. In this case n can adopt the value of a fractional number between 2 and 18. Preferably, the oxyalkylene block consists of ethylene oxide units, with the additional presence if desired of oxybutylene units in addition to the oxypropylene units. Oxyalkylene units having a carbon number of from 4 to 18 are preferred when, in addition, it is desired for the product to have oleophilic properties.
The average molecular weight of the phosphoric esters of the invention lies within the range from 300 to about 15,000 g/mol, preferably from 500 to 5000 g/mol. It can be determined with great ease by the customary methods of polymer analysis, both for the phosphoric esters and for the amphiphilic block copolymers. The ratio of m to o is from 1:50 to 50:1, preferably from 1:10 to 10:1 and, with particular preference, from 1:2 to 10:1.
Examples of suitable phosphoric esters are: 
Starting materials used to prepare the phosphoric esters of the invention are, accordingly, amphiphilic block copolymers of the general structures: 
respectively, where the radicals Rxe2x80x3 and Rxe2x80x2 and the indices m, k, n and o are as defined above.
These block copolymers are prepared by reacting the terminal hydroxyl group with a phosphorus compound which forms phosphoric esters, to give the phosphoric esters of the invention.
Block copolymers of this kind are described, for example, in DE-A-41 34 967. The polystyrene-b-polyalkylene oxide copolymers of type A-B are prepared by first subjecting styrene to free-radical polymerization in the presence of sufficient amounts of an initiator and of an amount, corresponding to the desired chain length, of a chain regulator which carries not only a mercapto group but also another functional group having an active hydrogen radical, generally a hydroxyl group, and subjecting the resulting polymer to an addition reaction at temperatures from 20 to 180xc2x0 C. with alkylene oxide until the desired molecular weight in the block B is reached.
The corresponding polystyrene oxide-b-polyalkylene oxide copolymers are prepared, starting from the starter alcohol Rxe2x80x2OH, by subjecting the corresponding alkylene oxides to a sequential addition reaction in accordance with the desired sequence and chain length of the individual segments so as to give a blocklike structure.
Both synthetic routes lead to amphiphilic block copolymers having a terminal hydroxyl group, both including, as an additional, characteristic structural element, a hydrophobic segment composed of aromatic groups. The processes described make it possible in a simple manner to adapt the chain lengths m and o of the individual segments, the overall molecular weight and the ratio m/o of aromatic to nonaromatic segments to the technical requirements of the particular application. For instance, products employed for applications in aqueous systems are preferably those whose polyalkylene oxide segment is composed of ethylene oxide units. Conversely, products having a relatively high proportion of styrene units and/or styrene oxide units have proven particularly suitable for dispersion processes in a very hydrophobic environment, such as, for example, paraffin oils, or in a polyolefin melt.
The reaction to give the phosphoric esters of the invention takes place by reaction of the terminal hydroxyl groups with a phosphorus compound which forms phosphoric esters, in a manner known per se. Examples of suitable phosphorus compounds are phosphorus pentoxide, phosphoryl chloride or polyphosphoric acids of the general formula Hn+2PnO3n+1. For the preparation of the phosphoric esters it is particularly preferred to employ a commercially available polyphosphoric acid (Merck) having a content of about 85% P4O10. The reaction generally takes place without solvent at temperatures from about 80 to 100xc2x0 C. To remove any traces of moisture present it is possible first of all to remove residues of water from the system using an inert solvent, such as toluene or xylene, for example, prior to the reaction with the polyphosphoric acid. Alternatively, in principle, the reaction can be carried out in the presence of solvents or solvent mixtures. This is always advantageous when the phosphoric esters of the invention have to be formulated in inert solvents or solvent mixtures in accordance with their subsequent use.
The extent of esterification of the terminal hydroxyl group of the amphiphilic block copolymers which is the target of esterification in the esterification reaction is preferably from 50 to 100%; with particular preference, esterification is quantitative. Depending on the amount of phosphorus compound which forms phosphoric esters, employed relative to the hydroxyl equivalent of the block copolymers, the products of the esterification are alternatively preferably monoesters, diesters, or mixtures of monoesters and diesters.
Depending on the pH of the medium employed, the phosphoric esters of the invention may also be present in partially or fully neutralized form.
The dispersants can either be applied directly to the solids that are to be dispersed or else can be added to the aqueous and/or organic medium. They can be distributed in pure form or as a masterbatch in relatively high concentration in an organic medium. It is of course also possible to employ the dispersants to be used in accordance with the invention together with further auxiliaries or dispersants, such as, for example, with the stearates known as dispersants.
Appropriate solids are mineral fillers, such as talc, calcium carbonate, dolomite, mica, wollastonite, kaolin, and mineral flame retardants, such as aluminum hydroxide or magnesium hydroxide. Suitable pigments are carbon black or titanium dioxide, the latter also being employable in finely divided form as a UV protectant in cosmetic formulations. Further dispersible solids are chemical blowing agents, such as azodicarbonamide, or mixtures of solid acids and carbonates.
The dispersants to be used in accordance with the invention can also be employed for dispersing ceramic materials in organic media, such as, for example, finely divided alumina, silicon carbide or silicon nitride.
Suitable organic media include polyethylene, polypropylene, polystyrene, polyamides, polyesters, poly(meth)acrylates, polyvinyl chloride, unsaturated polyesters, and liquid paraffins.
The dispersants of the invention are particularly suitable for enhancing the distribution of finely divided solids in elastomers, thermoplasts, thermosets and polymer blends.
The phosphoric esters of the invention have proven particularly suitable as dispersants for the preparation of highly filled SMC and BMC molding compounds. SMCs (sheet molding compounds) and BMCs (bulk molding compounds) consist of unsaturated polyester resins, a thermoplastic component, glass fibers, and fillers. The unsaturated polyester resin and the thermoplastic component (polystyrene is frequently used as the thermoplastic component) are usually dissolved in monomeric styrene which, in the course of processing by compression or injection molding, cures and forms a three-dimensional network structure with the unsaturated polyester resin. The addition of glass fibers leads to high tensile strength and rigidity; the fillers guarantee high compressive strength and are responsible, moreover, for good dimensional stability and low thermal expansion.
With the phosphoric esters of the invention a very low viscosity is achieved even at very high degrees of filling. The formulations feature absolute freedom from inhomogeneities and a high level of stability on storage.
In addition, the phosphoric esters of the invention can be used to prepare aqueous pigment pastes. For this purpose, use is made of from 0.1 to 200% by weight of the phosphoric esters, preferably from 0.5 to 100% by weight (based on the weight of the pigments). In the case of use in accordance with the invention the phosphoric esters can either be mixed beforehand with the pigments to be dispersed or else can be dissolved directly in the aqueous or solvent-containing dispersion medium prior to or simultaneously with the addition of pigments and any other solids.
Examples of pigments which can be mentioned in this context are organic and inorganic pigments, including carbon blacks.
As inorganic pigments mention may be made by way of example of titanium dioxides and iron oxides. Examples of organic pigments which may be considered are azo pigments, metal complex pigments, anthraquinonoid pigments, phthalocyanine pigments, polycyclic pigments, especially those of the thioindigo, quinacridone, dioxazine, pyrrolopyrrole, naphthalenetetracarboxylic acid, perylene, iso-amidolin(on)e, flavanthrone, pyranthrone or isoviolanthrone series. With particular preference, the dispersing additives of the invention are suitable for preparing aqueous carbon black (gas black) pastes.
Examples of fillers which can be dispersed in aqueous coating materials are those, for example, based on kaolin, talc, other silicates, chalk, glass fibers, glass beads, or metal powders.
Suitable coating systems in which the pigment pastes of the invention can be incorporated are any desired aqueous 1- or 2-component coating materials. Examples which may be mentioned are aqueous 1-component coating materials, such as those based on alkyd, acrylate, epoxy, polyvinyl acetate, polyester or polyurethane resins, or aqueous 2-component coating materials, examples being those based on hydroxyl-containing polyacrylate or polyester resins with melamine resins or, if desired, blocked polyisocyanate resins as crosslinkers. Similarly, polyepoxy systems may also be mentioned.
In the examples below, the preparation of the compounds to be used in accordance with the invention is described first of all. This is followed by performance examples demonstrating the properties of the compounds to be used in accordance with the invention and, for comparison, properties obtainable with some prior art products.
It is obvious and conventional to the skilled worker that these examples represent merely a selection of the possibilities which exist and are in no way to be regarded as a limitation.